In a plasma processing apparatus, the temperature of a substrate to be processed is increased by a plasma processing. Therefore, a base stand that supports the substrate is cooled by cooling water, and cooling gas is supplied to a gap between the substrate and the base stand. However, in a gas space including a supply path of the cooling gas, an abnormal discharge may easily occur due to a high frequency voltage applied at the plasma processing. When such abnormal discharge occurs, the plasma processing may not be stably performed.
Japanese Patent Laid-Open Publication No. H11-31680 discloses a plasma processing apparatus which employs a unique structure in a gas space so as to suppress the abnormal discharge. According to the unique structure, the electric field strength of a gas supply path may be weakened.